This invention relates to electric power switches, and more particularly to an improved commutation plate adapted to constrain the migration of the end of an arc formed on the movable contact of such a switch.
In a conventional power switch as schematically shown in FIG. 1 the end portion of the commutation plate 3 is bent in the form of an upwardly open U-shaped groove. An opening 3b extends across the bottom of the groove and up the side thereof opposite a grid confronting end plate 3a, and a contact 6 on a movable contact arm 5 is disposed in the opening 3b thus formed.
When an arc is generated at off-center position P on the end plate 3a, the values of the current components i.sub.1 and i.sub.2 flowing into the arc from the commutation plate 3 are substantially equal to each other, and the sum (i) of the components i.sub.1 and i.sub.2 is the arc current. As is apparent from FIG. 1, 1.sub.1 &gt; 1.sub.2 at position P. Accordingly, the force F.sub.1 of the current i.sub.1 affecting the arc is larger than the force F.sub.2 of the current i.sub.2, as a result of which the arc is driven in the direction of the force F.sub.1. The arc is thus shifted directly toward an arc box surrounding the grid, which is likely to damage the arc box.
Similar constructions are also disclosed in U.S. Pat. Ser. No. 4,237,355, and in commonly assigned copending application Ser. No. 380,314, filed May 20, 1982.